1. Field of the Invention
The present invention relates to a laminated glass windscreen having a predetermined taper angle and intended to be used at the same time as a reflector in a HUD system.
2. Discussion of the Background
It is known that the reflection of light rays from the surfaces of glass increases with the angle of incidence. In the case of windscreens which are fitted with a large angle of inclination, objects situated inside the vehicle and below the windscreen are visible to the driver in the windscreen, which acts as a mirror. This effect can be exploited, for example by projecting optical information onto the windscreen. In this regard, however, ordinary windscreens with parallel faces present the problem that the light rays, which are reflected both by the interior surface and by the exterior surface of the windscreen, present the observer with two images which are offset relative to one another.
It is known from EP 0 420 228 B1, hereby incorporated by reference, that this problem of double images can be avoided by using an intermediate layer with a wedge-shaped cross-section which makes the two reflecting surfaces of the windscreen form an angle such that the two reflected images appear superimposed to the driver's eyes. In this way, not only is a relatively sharp reflected image obtained, but the clarity of the image is also enhanced. However, the taper angle required of the intermediate layer for this purpose depends strongly on the angle at which the windscreen is fitted and on the position of the image projector in the vehicle, and therefore needs to be carefully adapted to each particular situation.
It is also known to use a thermoplastic intermediate sheet with a tinted filtering band during the manufacture of curved windscreens made of laminated glass with a filtering strip along the upper edge. The desired curvature of the filtering strip is then obtained by intentional irregular stretching of the sheet. This stretching, involving plastic deformation of the sheet, is carried out in order to adapt the profile of the filtering strip to that of the upper part of the laminated windscreen. Stretching in the shape of a circular arc leads to a taper on the long side of the curvature, which gives a sheet with a wedge-shaped cross-section. The taper angle of a sheet stretched in this way is determined by the radius required for the filtering strip. Therefore, the thermoplastic sheet with wedge-shaped cross-section formed in this way does not normally have the taper angle needed for a windscreen to be used as a reflector in a head-up display (HUD) system comprising two reflection surfaces which form a determined angle in order to superimpose the images.